Insulated conductor



June 16, 1942. A. c. BUERK ETAL INSULATED CONDUCTOR Filed June 21, 1941 Patented June 16, 1942 INSULATED CONDUCTOR Andrew C. Buerk and Edward Haberberger, St.

Marys, Pa., assignors to Stackpole Carbon Company, St. Marys, Pa., a corporation of Pennsylvania Application June 21, 1941, Serial No. 399,124

3 Claims.

This invention relates to insulated conductors and a method of insulating them, and more particularly to insulated shunt conductors of electric brushes used in generators, motors and the like.

The flexible conductors or cables of electric brushes and the like have been insulated in various ways heretofore, but much room has been left for improvement. For example, they have been coated with a liquid rubber compound or by rubber applied by anodic deposition. Either method is expensive and time consuming and produces an insulating covering which stiiTens the conductor appreciably because the rubber composition adheres to and is vulcanized to the conductor and conforms to the ridges and valleys formed by wire strands of which the cable is made. Another type of insulation used extensively on flexible conductors is cotton sleeving or tubing which is threaded over the conductors and clamped in place with bands of metal. This method also is time consuming, requiring cutting of the cotton sleeve, threading it on the conductor and then crimping a metal band on each end of the sleeve to hold it in place.

It is among the objects of this invention to provide a method of insulating flexible conductors which is rapid and relatively inexpensive, and which does not materially decrease the flexibility of the conductor. Another object is to provide an insulated conductor that remains flexible after the insulation has been applied to it.

In accordance with this invention a strip of elastic insulating material is wrapped and stretched around a flexible conductor and the edges of the strip are then secured together. Thus, the wrapping is held under tension on the conductors so that it is secured thereto solely by frictional engagement with it and therefore does not decrease the flexibility of the conductor materially. Preferably the adjoining edges of the strip of insulation are overlapped and fused together by the application of heat and pressure. When a shunt conductor is insulated in this manner the seam thus formed is made to extend along the space between the two portions of the conductor. Because of this the outer surface of the insulation is substantially smooth while its inner surface along the seam is provided with a rib, caused by the double thickness of the overlap, which projects into the valley between the two portions of the conductors.

The invention is illustrated in the accompanying drawing of which Fig. l is a perspective view of an electric brush with its shunt conductor resting on a strip of insulating material; Fig. 2 is a similar view showing the insulation stretched around part of the conductor; Fig. 3 is an enlarged end view showing the overlapping edges of the insulation about to be sealed together; Fig. 4 is an enlarged transverse section through the insulated conductor; and Fig. 5 is a perspective view of the insulated conductor.

Referring to the drawing for a disclosure of one way of applying the insulation to the conductor, an electric brush 1, for use in a generator, motor or the like, is provided in any suitable manner with a flexible shunt conductor 2, such as in the manner shown in Patent No. 2,043,474 to Howard B. Eynon. The two lengths or portions of this conductor, which preferably is in the form of a cable formed from twisted strands of wire, are then laid beside each other across the central portion of a substantially rectangular strip 3 of elastic or resilient insulating material as shown in Fig. 1. Rubber compositions or plasticized vinyl acetate compositions are especially suitable because of their thermoplastic properties which facilitate sealing the edges of the strip together as will be described presently.

The strip of insulation is then stretched around the conductor and fastened in place so that it remains under tension and is thereby held in position solely by its frictional engagement with the conductor. A simple but effective way of doing this is to lay the strip of insulation on a block 4 with the central portion of the strip overlying a recess 5 extending across the top of the block. The width or distance across this recess is slightly less than the full width of the conductor plus twice the thickness of the insulating strip so that when the conductor is pressed down into the recess the underlying insulating strip is squeezed between both sides of the conductor and the sides of the recess whereby the central portion of the strip is stretched down into the recess. The longitudinal marginal portions of the strip are left projecting above the blank at both sides of the conductor as shown in Fig. 2.

The next step is to fold these projecting edge portions over the top of the conductor. The strip is originally cut wide enough to have its edges meet, and preferably overlap a very small amount to provide more material at the junction for a stronger seam. The overlapping edges of the strip are pressed down tightly against each other by a heated tool 6, as shown in Fig. 3, so that this application of heat and pressure will fuse or seal the marginal portions of the strip together. The sealing usually requires from three to ten seconds for insulating material .030 of an inch thick As the conductor initially was placed on the center of the insulating strip the thickened portion that is produced at the seam by the double thickness of material forms an inside bead or rib I that extends along the valley between the two portions of the conductor and thereby leaves its outer surface, smooth, as shown in Figs. 4 and 5. If a single cable is insulated there will be a small ridge along the outside of the insulation where the seam is formed. 7 7

Due to our manner of applying insulation the wires of the cable remain unattached to the insulation so that they are free to slide on one another and against the insulation when flexed. As a result, the conductor remains substantially as flexible as it was before the insulation was applied. No cement or retaining clips are necessary to hold the insulation in place, while the insulation itself is inexpensive and quickly and easily applied,

According to the provisions of the patent statutes, we have explained the principle and method of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we

1. The combination with an electric brush and a flexible shunt conductor attached thereto, of a resilient wrapping surrounding the two portions of the conductor, said wrapping being under tension and held in position solely by frictional engagement with the conductor, and the edges of said wrapping being fused together with the seam between said two portions of the conductor.

2. The method of insulating the flexible shunt conductor of an electric brush, comprising stretching under tension a strip of resilient thermoplastic insulating material around both portions of the conductor with the edges of the strip overlapping between said portions, and then applying heat and pressure to the overlapped edges to seal them together with a substantially smooth outersurface and a rib along the inner surface between said portions of the conductor.

3. The method of insulating a flexible electrical conductor, comprising laying a strip of elastic insulating material over a recess that is narrower than the width of the conductor plus twice the thickness of the strip, laying the conductor on the strip, pressing the conductor with the underlying strip down into the recess to thereby stretch the strip laterally, folding the longitudinal edges of the strip into overlapping engagement over the conductor, and applying heat and pressure to said overlapping edges to seal them together, whereby the insulation is held on the conductor solely by its frictional engagement therewith.

ANDREW C. BUERK.

EDWARD HABERBERGER. 

